Wiring the rest of the Birmingham area is probably only going to be achieved as part of a "Big Bang" scheme like we have seen in Scotland with the Central Belt, where the associated routes were added on to the original EGIP project.
With the Snow Hill network being pretty integrated and contained, any transformation will be to the benefit of the whole route, but the extent of wiring could be up for discussion.
The central core would be a worthwhile project, with initial thoughts (especially if it falls to WM funding it) of taking wires out to Stourbridge and Dorridge/Whitlocks End with current service patterns probably strong enough to drive an extension to Kidderminster, and if battery technology has come far enough this could be a worthwhile half way measure for the unwired arms to Worcester, Leamington and Stratford upon Avon (15, 12.75 and 15.5 or 17 miles respectively) to be covered this way.
Clearly utopia would see a more regional scheme to get wires out to the above three (along with Bromsgrove to Droitwich and Hatton Triangle to Wimcote) and be a kick start to further follow on schemes